What’s the latest on breakthrough Covid cases?

Jul 28, 2021

The Grand Central Market in Los Angeles after the recent mask mandate went into effect. Some people are masked while others are not.

By David Leonhardt

Breakthrough infections — in which vaccinated people nonetheless get the Covid-19 virus — are one of those vexing topics that can be difficult to put in perspective.
On the one hand, breakthrough infections are obviously occurring. They’ve happened to the New York Yankees and to White House officials, as well at summer gatherings in Massachusetts, Oklahoma and elsewhere. My colleague Liam Stack recently got sick with a breakthrough infection (and I’ll tell you his story below).

On the other hand, the scale of breakthrough infections remains unclear. Are they a significant reason that cases are now surging in the U.S. — and a reason for vaccinated people to be concerned? Or are breakthrough infections rare exceptions that receive outsize attention?

Those are two very different scenarios. If breakthrough infections are an important source of Covid spread, it would suggest that vaccinated people should resume some of their previous precautions, like avoiding crowded places. If Covid is instead spreading overwhelmingly among the unvaccinated, it would suggest that the behavior of the vaccinated doesn’t matter very much; the only reliable way to reduce caseloads would involve more vaccinations.

I’m going to warn you up front that I don’t have a definitive answer for you. “There’s a lot of uncertainty right now,” as Natalie Dean, a biostatistician at Emory University, told me. But there is some evidence that can help you think through the situation while scientists collect more data.

What we know
Let’s start with a few facts that are clear:

• Vaccinated people are nearly guaranteed not to be hospitalized or killed by Covid.
• Among children under 12, who remain ineligible for the vaccine, serious forms of Covid are also extremely rare. Children face bigger risks when they ride in a car.
• The Delta variant does not appear to change either of those facts.
• Millions of unvaccinated American adults are vulnerable to hospitalization or death from Covid.

Given all of this, the most effective Covid-fighting strategy has not changed, experts say: “Shots in arms,” as my colleague Apoorva Mandavilli writes. Or as Dean says, “The biggest problem is that there are a lot of people with no protection.”

And there are measures that would almost certainly increase vaccinations: Full F.D.A. approval (which hasn’t happened despite public endorsements of the vaccines by the F.D.A.’s leaders); vaccine mandates from employers and local governments; and pro-vaccination messages from Republican politicians, professional athletes and other people who have credibility among vaccine skeptics. Any of these steps would almost certainly have a bigger effect than behavioral changes among the vaccinated.

Still, I understand why many vaccinated people are wondering if they should change their behavior. I feel the same way. I don’t want to contribute to the spread of the virus, and I would rather not contract even a modest version of Covid.

Among other reasons, the risks of “long Covid” remain uncertain. Yes, those risks get exaggerated sometimes: Many viruses, like influenza, cause long-term symptoms, and some of the focus on long Covid stems from society’s current obsession with all things Covid. There is still no rigorous study that compares long Covid with “long flu.” But long Covid is probably worse, which argues for caution.

What we don’t know
How common, then, are breakthrough infections?

One reason for optimism is the recent trend among the most vaccinated segments of society: older people. About 80 percent of Americans over age 65 have been fully vaccinated. This chart looks at the U.S. since late June, when cases began rising:

This chart looks at England — where more than 90 percent of older people are vaccinated — since late May, when cases began rising there:

As you can see, new cases have risen only modestly among people over 65, suggesting that breakthrough infections are rare. “I think people who are vaccinated are not, on a population level, major contributors to the transmission of the disease,” Dr. David Dowdy, a Johns Hopkins University epidemiologist, told me.

Part of the reason is that vaccinated people are both less likely to get infected and less likely to pass on the virus even if they do get infected, scientists say. A vaccinated person without Covid symptoms seems especially unlikely to infect somebody else.

“What is clear is that people who are vaccinated and have symptomatic breakthrough infections can transmit it to other people,” Dr. Ashish Jha of Brown University said. “What is not at all clear is whether vaccinated asymptomatic people can transmit it. And my best guess is no — or not very often.”

He added: “I’m not worried about an asymptomatic vaccinated person spreading it to me.”
Of course, a vaccinated person can still get the virus from somebody who has symptoms or hasn’t been vaccinated. Liam Stack, a Times reporter who covers religion, was fully vaccinated by April but nonetheless caught the virus in June, probably socializing with friends, either at a bar or a beach house, he says.

“It was not the sickest I’ve ever been, but it was very disruptive,” he told me. He was sick for a full week, with flulike symptoms, including congestion, muscle aches and fatigue. One day, he took a three-hour nap around lunchtime, followed by a two-hour nap before dinner.

Liam is feeling better now, and, as far as he knows, none of his friends or family members contracted the virus from him. But he does not recommend the experience. “It was unpleasant,” he said.

The bottom line
Different vaccinated people are going to make different decisions, and that’s OK. I find the risk of breakthrough infections to be small enough that I’m not going to make major changes to my behavior.

I would feel differently if I lived in a community with a lower vaccination rate — or if I lived with somebody who was vulnerable to Covid because of an immunodeficiency. And the current surge in cases has changed my thinking. I will again wear a mask sometimes when in close contact with strangers, even if it has little tangible effect. The main reason to do so, as Dowdy said, is to contribute to a shared sense that we have entered a worrisome new phase of the pandemic.

It’s also important that the country not respond in ways that would do more harm than good — say, by delaying the full reopening of schools, Dowdy added. For vaccinated people, Covid still represents a very small risk, and the cost of our response should not exceed the benefits.

But when cases are surging, as they are now, our approach to Covid should be different than when they are plunging.

Credit: New York Times Morning Letter